Microfiche film systems have enjoyed tremendous success in the marketplace because with these systems a great quantity of information may be stored on a relatively small piece of flat film and retrieved easily with the use of a film reader. In most systems, an image of documentary information is reduced in size by photographic techniques and reproduced on a sheet of film. To retrieve the information, the film sheet is usually placed beneath a glass plate in a reader. A lens located over the glass plate magnifies the image, and a light projects the magnified image on to a screen. To retrieve other information on the film, the operator moves the glass plate and film beneath the lens to another part of the film area.
It is usually necessary to focus the image each time a new sheet of film is placed beneath the glass plate, and each time the glass plate is moved, due to inherent irregularities in the manufacture of the microfilm reader and the upper surface of the glass plate on which the lens housing rides. Re-focusing is generally accomplished by adjusting the lens in the vertical direction with respect to the film and glass plate.
To properly focus the image, the lens must lie flat on the surface of the glass plate. If the glass plate rises or dips even slightly, the lens must be re-adjusted for the change in attitude. To accomplish this, the lens housing is typically universally mounted on gimbals, such as those described in U.S. Pat. No. 3,634,005. The gimbals enable the lens housing to adjust to changes in the attitude of the surface of the glass plate as the plate is moved from location to location by permitting pivotal movement of the lens in any direction in the horizontal plane defined generally by the top surface of the glass plate.
Generally, apparatus for adjusting the lens vertically includes, among other things, a shaft fixed to the frame of the reader and a knob attached to the shaft along an outside edge of the frame which enable the operator to conveniently adjust the lens to focus the image. However, the operator must be able to adjust the lens regardless of the attitude of the lens with respect to the horizontal plane. Also, movement of the lens with respect to the horizontal plane must not be appreciably impaired by the lens adjusting apparatus, or the advantages gained through the use of the universal mounting may be lost. Thus, there is a need for image focusing apparatus which functions properly when the lens tilts in various directions, without appreciably impairing the movement of the lens.
Accordingly, an object of the present invention is to provide new and improved image focusing assemblies for microfiche film readers and other optical systems.
Another object is to provide new and improved image focusing apparatus for microfiche film readers in which the lens holding mechanism is universally mounted, such as on gimbals, and the image focusing apparatus does not interfere with the action of the gimbals.
Yet another object is to provide new and improved image focusing assemblies which are inexpensive to manufacture and assemble.
Still another object is to provide a new and improved image focusing apparatus which is operable over a range of lens angles with respect to the horizontal plane.
In keeping with one aspect of the present invention, an image focusing apparatus for microfiche film readers and other optical systems having a lens holding apparatus with a universal mounting is provided which has a lens-adjusting assembly in the lens holding apparatus, a shaft simultaneously slidably and pivotally connected to the lens adjusting assembly, a knob on the shaft, and a shaft holder which holds the shaft with respect to the reader. The lens may be adjusted vertically by turning the knob regardless of the angular disposition of the lens-adjusting device with respect to the shaft.